To examine structure-function relationships in biological membranes, presently incompletely understood, we will continue to study phagocytosis. This biological event is accompanied by profound alterations in the membranes of both the phagocyte and the ingested microorganisms. We will specifically continue the characterization and purification of a potent bactericidal factor of polymorphonuclear leukocytes, which in highly purified form also exhibits phospholipase A2 and bacterial envelope permeability increasing activities. BIBLIOGRAPHIC REFERENCES: Beckerdite-Quagliata, S., Simberkoff, M. and Elsbach, P. Effects of human and rabbit serum on viability, permeability and envelope lipids of Serratia marcescens. Inf. and Immun. 11:758-766, 1975. Mooney, C. and Elsbach, P. Altered phospholipid metabolism in Escherichia coli accompanying killing by disrupted granulocytes. Inf. and Immun. 11:1269-1277, 1975.